Sort in javascript

sort.js

[[2, 37], [1, 40], [3, 39], [0, 36]].sort(([,a],[,b]) => {
  count;
  console.log(count + " a: " + a + ", b: " + b);
  count++;
  return a-b})

/*

0 a: 40, b: 37
1 a: 39, b: 40
2 a: 39, b: 40
3 a: 39, b: 37
4 a: 36, b: 39
5 a: 36, b: 37

0: [0, 36]
1: [2, 37]
2: [3, 39]
3: [1, 40]

*/